The basis of combinatorial chemistry is to form large libraries of molecules in a single process step, instead of synthesizing compounds individually, as was hitherto traditional, and to identify the most promising compounds by high throughput screening of the compounds in the libraries. Although originally used mainly in the pharmaceutical industry, it has since found more widespread use throughout the chemical industries, and has been extended to the synthesis of inorganic materials. By application of the present invention, it is possible to apply the techniques of combinatorial chemistry to the preparation of metal alloys and inorganic materials by vapour deposition.
Combinatorial chemistry, as it applies to the present invention, requires the deposition of materials in relative amounts that vary progressively in at least one direction along a substrate. U.S. Pat. No. 6,045,671 discloses a method of achieving this in which a shadow mask or masks is or are moved directly in front of a substrate between a source (of the vapour deposited material) and the substrate, so as to expose positions on the substrate to increasing amounts of material in proportion to the time that these positions lie in direct line of sight of the source. Necessarily, such an arrangement can only be used with a single source at one time. Accordingly, if this process is to be used to produce a mixture of materials, as is necessary for combinatorial chemistry, the coated substrate has to be subjected to a second pass using a second source, and then the deposited material has to be mixed in some way without disturbing the relative concentrations of the materials at different positions on the substrate. According to U.S. Pat. No. 6,045,671, this is done by heated the deposited materials. However, in practice, the effectiveness of heating as a method of mixing can be limited, and it cannot be used at all with heat-sensitive materials.
There is, therefore, a need in combinatorial chemistry for a method for the simultaneous deposition of two or more materials in uniformly varying amounts, the amounts varying according to a pre-arranged pattern according to location on the substrate.